OpenFOAM中热物理量的计算（二）

在求解温度的过程中到了显焓Hs(p,t)和比热Cp(p,t)函数，其计算方法在<constant>/thermophysicalProperties中指定，通常采用janaf多项式计算

// $FOAM_SRCthermophysicalModels/specie/thermo/janaf/janafThermoI.H
template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Cp
(
    const scalar p,
    const scalar T
) const
{
    const coeffArray& a = coeffs(T);
    return
        ((((a[4]*T + a[3])*T + a[2])*T + a[1])*T + a[0])
      + EquationOfState::Cp(p, T);
}


template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Ha
(
    const scalar p,
    const scalar T
) const
{
    const coeffArray& a = coeffs(T);
    return
    (
        ((((a[4]/5.0*T + a[3]/4.0)*T + a[2]/3.0)*T + a[1]/2.0)*T + a[0])*T
      + a[5]
    ) + EquationOfState::H(p, T);
}


template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Hs
(
    const scalar p,
    const scalar T
) const
{
    return Ha(p, T) - Hc();
}


template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Hc() const
{
    const coeffArray& a = lowCpCoeffs_;
    return
    (
        (
            (((a[4]/5.0*Tstd + a[3]/4.0)*Tstd + a[2]/3.0)*Tstd + a[1]/2.0)*Tstd
          + a[0]
        )*Tstd + a[5]
    );
}

理想气体的计算公式在

// $FOAM_SRC/thermophysicalModels/specie/equationOfState/perfectGas
template<class Specie>
inline Foam::scalar Foam::perfectGas<Specie>::rho(scalar p, scalar T) const
{
    return p/(this->R()*T);
}


template<class Specie>
inline Foam::scalar Foam::perfectGas<Specie>::H(scalar p, scalar T) const
{
    return 0;
}


template<class Specie>
inline Foam::scalar Foam::perfectGas<Specie>::Cp(scalar p, scalar T) const
{
    return 0;
}

根据温度的不同，janaf选用高温和低温两组不同的系数来计算热物性参数，例如，当温度大于Tcommon（一般为1000K）时采用高温度的多项式系数，当温度小于Tcommon时，采用低温度的多项式系数。

// thermophysicalModels/specie/thermo/janaf/janafThermoI.H
template<class EquationOfState>
inline const typename Foam::janafThermo<EquationOfState>::coeffArray&
Foam::janafThermo<EquationOfState>::coeffs
(
    const scalar T
) const
{
    if (T < Tcommon_)
    {
        return lowCpCoeffs_;
    }
    else
    {
        return highCpCoeffs_;
    }
}

其中比热的计算方法：

template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Cp
(
    const scalar p,
    const scalar T
) const
{
    const coeffArray& a = coeffs(T);
    return
        ((((a[4]*T + a[3])*T + a[2])*T + a[1])*T + a[0])
      + EquationOfState::Cp(p, T);
}

总焓的计算方法

template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Ha
(
    const scalar p,
    const scalar T
) const
{
    const coeffArray& a = coeffs(T);
    return
    (
        ((((a[4]/5.0*T + a[3]/4.0)*T + a[2]/3.0)*T + a[1]/2.0)*T + a[0])*T
      + a[5]
    ) + EquationOfState::H(p, T);
}

显焓的计算方法

template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Hs
(
    const scalar p,
    const scalar T
) const
{
    return Ha(p, T) - Hc();
}

生成焓的计算方法：

template<class EquationOfState>
inline Foam::scalar Foam::janafThermo<EquationOfState>::Hc() const
{
    const coeffArray& a = lowCpCoeffs_;
    return
    (
        (
            (((a[4]/5.0*Tstd + a[3]/4.0)*Tstd + a[2]/3.0)*Tstd + a[1]/2.0)*Tstd
          + a[0]
        )*Tstd + a[5]
    );
}

可以明显地看出，显焓=总焓-生成焓